Flywheel assembly for internal combustion engine

ABSTRACT

A crankshaft assembly for an internal combustion engine includes a crankshaft, an elastic member fixed to the crankshaft, and a flywheel fixed to the elastic member such that the flywheel is supported in an elastic relationship with the crankshaft. The elastic member has a rigidity in its rotating direction large enough to effectively transmit a driving power to a transmission through a clutch. On the other hand, the elastic member has a rigidity in an axial direction of the crankshaft small enough to shift a resonance frequency of a bending vibration out of a target frequency band of a forced vibration, while ensuring to prevent a failure of disengagement of the clutch.

This application is a continuation of application Ser. No. 07/485,659filed Feb. 27, 1990 now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a crankshaft assembly including aflywheel, for an internal combustion engine. More specifically, thepresent invention relates to a crankshaft assembly for an internalcombustion engine, which can effectively shift a resonance frequency ofa flexural or bending vibration of the crankshaft assembly out of atarget frequency band of a forced vibration which results such as duringacceleration of a vehicle so as to effectively prevent occurrence of athick sound or noise in an engine room, while ensuring a quick responsefor clutch engaging and disengaging operations, and/or which can preventoccurrence of a fore and aft vibration of a vehicle floor at the time ofengagement of the clutch.

2. Description of the Background Art

In a known crankshaft assembly for an internal combustion engine, aflywheel is directly connected to a crankshaft to use a mass of theflywheel mainly for reducing a torsional vibration generated in arotating direction of the crankshaft assembly due to periodic torquefluctuation. However, the mass of the flywheel tends to generate aflexural or bending vibration in an axial direction of the crankshaftwhich causes a thick sound or noise in an engine room and thus in avehicle compartment for an automotive vehicle, particularly at the timeof the acceleration of the vehicle.

Accordingly, there has been proposed a crankshaft assembly such asdisclosed in Second Japanese Patent Publication No. 57-58542, whereinthe flywheel is connected to the crankshaft through an elastic orflexible plate. The elastic plate has a rigidity in its rotatingdirection large enough for effectively transmitting the power betweenthe crankshaft and a transmission through a clutch, while the elasticplate has a rigidity in the axial direction small enough for shifting aresonance frequency of the bending vibration out of a frequency band ofa forced vibration which results during the most frequently used enginespeed (4,000 rpm) so as to overcome the above-noted problem.

However, the background art as mentioned above has the followingproblems.

When the rigidity of the elastic plate in the axial direction(hereinafter referred to as “the axial rigidity”) is too small, a clutchstroke for engaging and disengaging the clutch is likely to becomelarger, resulting in a delayed response of the clutch engaging anddisengaging operations leading particularly to failure of the clutchdisengagement which is likely to cause such as an engine stall. On theother hand, when the axial rigidity of the elastic plate is too large,the deviation of the resonance frequency of the bending vibration fromthe target frequency band of the forced vibration can not be ensured.

Further, in the background art, when the flywheel is rotated, an axialrun-out occurs on an engaging surface of the flywheel with a clutchfacing of a clutch disc provided adjacent to the flywheel, due to aprocessing error and an assembling error of the elastic plate and theflywheel. Accordingly, when the clutch is engaged, a vibration isgenerated by a combination of the run-out of the engaging surface of theflywheel and the torque fluctuation of the engine, which is amplified bya vibration generated by the combustion in the engine cylinders andcorresponding movement of associated members so as to cause a fore andaft vibration of the vehicle floor. Such vibration is uncomfortable forthe driver and passengers in the vehicle compartment.

SUMMARY OF THE INVENTION

Therefore, it is an object of the present invention to provide acrankshaft assembly for an internal combustion engine that can eliminatethe above-noted defects inherent in the background art.

It is another object of the present invention to provide a crankshaftassembly for an internal combustion engine that can effectively shift aresonance frequency of a flexural or bending vibration of the crankshaftassembly out of a target frequency band of a forced vibration,particularly out of a target frequency band which results duringacceleration of a vehicle so as to effectively prevent occurrence of athick sound or noise in an engine room, while ensuring a quick responseof the clutch engagement and disengagement operations so as to preventparticularly the failure of the clutch disengagement which is likely tocause such as an engine stall.

It is still another object of the present invention to provide acrankshaft assembly for an internal combustion engine that can preventoccurrence of a fore and aft vibration of a vehicle floor at the time ofthe engagement of the clutch by effectively eliminating an axial run-outof an engaging surface of a flywheel with a clutch facing generatedduring rotation of the flywheel.

To accomplish the above mentioned and other objects, according to oneaspect of the present invention, a crankshaft assembly for an internalcombustion engine comprises a crankshaft for transmitting a drivingpower to a transmission through a clutch, an elastic member fixed to thecrankshaft, and a flywheel fixed to the elastic member such that theflywheel is supported in an elastic relationship with the crankshaft.

The flywheel has an engageable surface at a side opposite to the elasticmember in an axial direction of the crankshaft, and the engageablesurface is engageable with an associated member of the clutch to receivea load therefrom in the axial direction when the engageable surface isengaged with the associated member of the clutch.

The elastic member has a first predetermined rigidity in its rotatingdirection, the first predetermined rigidity being large enough toeffectively transmit the driving power to the transmission through theclutch. On the other hand, the elastic member has a second predeterminedrigidity in the axial direction, the second predetermined rigidity beingsmall enough to shift a resonance frequency of a bending vibration outof a target frequency band of a forced vibration, while ensuring toprevent a failure of disengagement between the engageable surface of theflywheel and the associated member of the clutch.

According to another aspect of the present invention, a method forforming a crankshaft assembly for an internal combustion enginecomprises steps of fixing a flywheel to an elastic member to form aunit, assembling the unit onto the crankshaft with the elastic membermounted onto the crankshaft so as to support the flywheel in an elasticrelationship with the crankshaft, and processing an engageable surfaceof the flywheel, which is engageable with an associated member of aclutch, based on an assembled condition between the elastic member andthe crankshaft so as to minimize an axial run-out of the engageablesurface.

According to still another aspect of the present invention, a crankshaftassembly for an internal combustion engine comprises a crankshaft fortransmitting a driving power to a transmission through a clutch, anelastic member fixed to the crankshaft, and a flywheel fixed to theelastic member such that the flywheel is supported in an elasticrelationship with the crankshaft.

The flywheel has an engageable surface at a side opposite to the elasticmember in an axial direction of the crankshaft, and the engageablesurface is engageable with an associated member of the clutch to controltransmission of the driving power between the crankshaft and thetransmission.

The engageable surface is designed to have an axial run-out which is nomore than 0.1 mm for ensuring a smooth engagement with the associatedmember of the clutch.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood more fully from the detaileddescription given hereinbelow and from the accompanying drawings of thepreferred embodiment of the invention, which are given by way of exampleonly, and are not intended to be limitative of the present invention.

In the drawings:

FIG. 1 is a longitudinal cross section of a crankshaft assembly for aninternal combustion engine according to a first preferred embodiment ofthe present invention;

FIG. 2 is a graph of vibration level versus frequency showing a shift ofa resonance frequency of a flexural or bending vibration by changing arigidity of an elastic or flexible plate in an axial direction of acrankshaft;

FIG. 3 is a longitudinal cross section of a crankshaft assembly fopforan internal combustion engine according to a second preferred embodimentof the present invention; and

FIG. 4 is a graph of fore and aft vibration of vehicle floor versusflywheel run-out amount, showing a relationship between an amount of anaxial run-out of a flywheel and a fore and aft vibration of a vehiclefloor.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Now, a crankshaft flywheel assembly for an internal combustion engineaccording to preferred embodiments of the present invention will bedescribed hereinbelow with reference to FIGS. 1 to 4.

FIG. 1 shows a first preferred embodiment of the present invention. Anengine crankshaft 1 is connected to pistons through respectiveconnecting rods in a known manner for receiving the driving powertherefrom. An elastic plate 2of this example is substantially of a discshape, and is fixed, at its inner portion 2f, to one shaft end of thecrankshaft 1 by a plurality of bolts 3. The elastic plate 2is formed atitshas an outer peripheral edge portion 2b which is formed with anaxially extending sectionflange 2a to which a ring gear R is fixed. Thering gear R engages with pinion gears of an engine starter motor fortransmitting the driving power from the engine starter motor to thecrankshaft 1 when starting the engine.

An annular reinforcing member 4 is disposed between the elastic plate 2and heads of the bolts 3. The reinforcing member 4 is formed at itsouter peripheral edge portion with a received portion 4a which is inthis example cylindrical section 4a extending and extends in an axialdirection of the crankshaft 1. and with The reinforcing member 4 of thisexample further has a radially outwardly extending section flange 4b inthe form of an outward flange, as shown in FIG. 1. The inner portion 2fof the elastic plate 2 is clamped between the reinforcing member 4 andthe shaft end of the crankshaft 1.

A flywheel body 5 of an annular shape is fixed to the elastic plate 2 attheir respective outer peripheral edge portions 5a and 2b through aplurality of bolts 6 and corresponding reinforcing members 7 disposedbetween the elastic plate 2 and heads of the bolts 6. The annularflywheel body 5 has a stepped inner peripheral edge surface defining amounting opening 5b for receiving the reinforcing member 4 therein. Thestepped inner peripheral edge surface has a first section 5c extendingaxially, a second section 5d extending radially outward from the firstsection 5c and a third section 5e extending axially from the secondsection 5d. The axial section 4a of the reinforcing member 4 is in aslidable contact with the first section 5c of the flywheel body 5, andthe radial section 4b of the reinforcing member 4 is spaced from thesecond section 5d of the flywheel body 5 by a predetermined distance forallowing an axial movement of the flywheel along with the elastic plate2. A radially extending inner surface 5f of the flywheel facing theelastic plate 2 is spaced apart from the elastic plate 2 by apredetermined distance for ensuring an elasticity of the elastic plate2. In other words, a first clearance or second free space is providedbetween inner surface 5f and the elastic plate 2 for allowing axialmovement of the flywheel body.

The flywheel body 5 further includes a radially extending side surface5g at a side axially opposite to the radial side surface 5f or theelastic plate 2. The radial radially extending side surface 5g is anengaging surface which is engageable with a clutch facing 8 of a clutchdisc 9 of a clutch in a known manner so as to control the transmissionof the power between the crankshaft 1 and a transmission.

A rigidity of the elastic plate 2 in its rotating direction (hereinafterreferred to as “the circumferential rigidity”) is set large enough foreffectively transmitting the power between the crankshaft 1 and thetransmission through the clutch, while a rigidity of the elastic plate 2in the axial direction (hereinafter referred to as “the axial rigidity”)is set small enough for shifting a resonance frequency of the flexuralor bending vibration out of a frequency band of a forced vibration whichresults during the acceleration of the engine.

As described in the background art, when the axial rigidity of theelastic plate is too small, a clutch stroke for engaging and disengagingthe clutch becomes larger, i.e. a clutch stroke loss gets larger,resulting in delayed response of the clutch engaging and disengagingoperations leading particularly to the failure of the clutchdisengagement which is likely to cause such as an engine stall. On theother hand, when the axial rigidity of the elastic plate is too large,the deviation of the resonance frequency of the bending vibration fromthe target frequency band of the forced vibration can not be attained.

To overcome the above-noted problem, the axial rigidity of the elasticplate 2 in this embodiment is set to 600 kg/mm to 2200 kg/mm, wherein anaxial displacement of the radial surface 5g of the flywheel 5 is no morethan 1 mm when an axial load or force 600 kg to 2200 kg is applied tothe radial surface 5g. By selecting a value of the axial rigidity of theelastic plate 2 within the foregoing range, not only is the failure ofthe clutch disengagement effectively prevented, but also the deviationof the resonance frequency of the bending vibration from the frequencyband of the forced vibration, during the acceleration of the engine inthis embodiment, is effectively attained so as to prevent generation ofthe thick sound or noise in the engine room.

Specifically, it is confirmed that the failure of the clutchdisengagement, i.e. the failure of the disengagement between the radialsurface 5g of the flywheel and the clutch facing 8 of the clutch disc 9,happens when an axial displacement of the radial surface 5g at the timeof engagement with the clutch facing 8 exceeds 5% of a normal clutchstroke (normally at 7 mm to 8 mm) fur for engaging and disengaging theclutch. The normal clutch stroke is a distance between the radialsurface 5g of the flywheel body 5 and the clutch facing 8 in adisengagement or released condition of the clutch. Accordingly,considering that an axial load applied to the flywheel body 5 throughthe clutch facing 8 is normally at 150 kg to 200 kg, the lower limitvalue 600 kg/mm of the axial rigidity of the elastic plate is selected,wherein the axial displacement of the radial surface 5g is within 5% ofthe normal clutch stroke when applied with the axial load 150 kg to 200kg, as shown in TABLE 1.

TABLE 1 AXIAL AXIAL LOAD AXIAL RIGIDITY DISPLACEMENT 150 kg 500 kg/mm0.30 mm (3.8 to 4.3%) 200 kg 500 kg/mm 0.40 mm (5.0 to 5.7%) 150 kg 600kg/mm 0.25 mm (3.1 to 3.6%) 200 kg 600 kg/mm 0.33 mm (4.1 to 4.7%) 150kg 700 kg/mm 0.21 mm (2.6 to 3.0%) 200 kg 700 kg/mm 0.29 mm (3.6 to4.1%)

(wherein, percentage denotes a rate of the axial displacement relativeto the normal clutch stroke which is 7 to 8 mm)

As seen from TABLE 1, the lower limit value 600 kg/mm of the axialrigidity of the elastic plate 2 ensures the axial displacement of theradial surface 5g of the flywheel body 5 within 5% of the normal clutchstroke, i.e. the axial displacement of the radial surface 5g is between0.25 to 0.33 mm or between 3.1 to 4.7% relative to the normal clutchstroke when applied with the normal axial load at 150 to 200 kg throughthe clutch facing 8, so that the failure of the clutch disengagement iseffectively prevented. Naturally, the larger the axial rigidity of theelastic plate gets, the smaller the axial displacement of the flywheelgets.

Now, the axial rigidity of the elastic plate 2 will be considered inview of shifting of the resonance frequency of the bending vibration outof a frequency band of a forced vibration which results during theacceleration of the engine where the sound or noise generated by thebending vibration is the most significant. It is confirmed that thesound or noise generated by the bending vibration is effectively reducedwhen the resonance frequency is shifted out of the frequency band of theforced vibration during the acceleration of the engine.

FIG. 2 is a graph of bending vibration level versus frequency showing aresult of experiments using various elastic plates having differentaxial rigidities. The frequency band of the forced vibration during theacceleration of the engine is 200 Hz to 500 Hz. In FIG. 2, a line Aoshows a relationship between the frequency and the bending vibrationlevel without using the elastic plate, i.e. the flywheel is directlyconnected to the crankshaft. As can be seen, a resonance frequency ofthe line Ao is within 200 Hz to 500 Hz, which causes the sound or noiseproblem. A line A1 is derived by the elastic plate having the axialrigidity of 2200 kg/mm, a line A2 is derived by the elastic plate havingthe axial rigidity of 1700 kg/mm, line A3 is derived by the elasticplate having the axial rigidity of 1200 kg/mm, and a line A4 is derivedby the elastic plate having the axial rigidity of 1000 kg/mm. As can beseen, the resonance frequency of each of the lines A1 to A4 is shiftedout of the frequency band 200 Hz to 500 Hz, and further, the vibrationlevel of each of the lines A1 to A4 is considerably lower than the lineAo within the frequency band 200 Hz to 500 Hz. Though the line A1 has avibration level higher than the line Ao around 200 Hz, this happens in avery small range of frequency. Accordingly, the value 2200 kg/mm isselected as an upper limit value of the axial rigidity of the elasticplate, and the value 1700 kg/mm is selected as a more preferable upperlimit value of the axial rigidity.

In light of the above, the axial rigidity of the elastic plate 2 in thisembodiment is selected at 600 kg/mm to 2200 kg/mm, and preferably at 600kg/mm to 1700 kg/mm.

As understood from the above description, this first embodiment, whenthe crankshaft 1 is rotated, the flywheel body 5 is ensured to rotatewith the crankshaft 1 by means of the large circumferential rigidity ofthe elastic plate 2. When the clutch is engaged and the engine isaccelerated, the driving power is transmitted to the transmission with avery low bending vibration level by means of the axial rigidity of theelastic plate being no more than 2200 kg/mm, so that the vehiclecompartment can be kept quiet. On the other hand, when the clutch isdisengaged, since the axial displacement of the flywheel is no more than5% of the normal clutch stroke by means of the axial rigidity of theelastic plate being no less than 600 kg/mm, the failure of thedisengagement of the clutch is effectively prevented.

FIG. 3 shows a crankshaftflywheel assembly for an internal combustionengine according to a second embodiment of the present invention. InFIG. 3, the same or like parts or members are denoted by the samereference numerals. In the following description, explanations of thosesame or like members will be omitted to avoid redundant description.Further, though the clutch assembly is not shown in FIG. 3, the sameclutch assembly including the clutch disc 9 and the clutch facing 8 isprovided in the same manner as in FIG. 1.

In FIG. 3, the crankshaft 1 includes a stepped end surface having afirst section 1a extending radially inward from its outer peripheraledge, a second section 1b extending axially from the inward end of thefirst section 1a toward the clutch disc 9, and a third circular section1c extending radially from the second section 1b. The elastic plate 2 isof an annular shape having a mounting opening at its center forreceiving the second section 1b therethrough. The elastic plate 2 isfixed to the crankshaft 1 with its axially extending inward end 2cfacing the second section of the crankshaft 1 and with its radiallyextending inward end portion 2d facing the first section of thecrankshaft. The other structure is substantially the same as in FIG. 1.

As mentioned in the background art, when the flywheel body 5 is rotatedthrough the crankshaft 1, an axial run-out is generated on the radialengaging surface 5g due to the processing error and the assembling errorof the elastic plate 2 and the flywheel body 5 to cause the vibrationwhen the clutch is engaged. The vibration further causes the fore andaft vibration of the vehicle floor.

In order to overcome the above-noted problem, in this embodiment, theradial engaging surface 5g is processed in a manner to make an amount ofthe axial run-out no more than 0.1 mm. Specifically, the processing ofthe radial engaging surface 5g is performed in the following manner.

The flywheel body 5 is first fixed to the elastic plate 2 by the bolts6. Then, this unit is assembled to the crankshaft 1 with the axiallyextending inward end 2c of the elastic plate 2 facing the second section1b of the crankshaft 1 and with the radially extending inward endportion 2d facing the first section 1a of the crankshaft. Then, theradial engaging surface 5g is processed based on the assembled conditionbetween the axially extending inward end 2c and the second section 1band/or between the radially extending inward end portion 2d and thefirst section 1a to make the axial run-out of the radial surface 5g nomore than 0.1 mm.

By using the above-noted manner, the radial engaging surface 5g iseasily and precisely processed to make the amount of the axial run-outno more than 0.1 mm.

FIG. 4 is a graph of axial run-out amount of flywheel (radial engagingsurface 5g) versus fore and aft vibration of vehicle floor showing aresult of experiments. It is confirmed that the fore and aft vibrationof the vehicle floor which does not give a uncomfortable feeling to ahuman body is normally no more than 0.1 G (gravitational acceleration).As can be seen from FIG. 4, a fore and aft vibration of the vehiclefloor is substantially in direct proportion to an amount of the axialrun-out of the radial engaging surface 5g, and the fore and aftvibration becomes no more than 0.1 G when the axial run-out becomes nomore than 0.1 mm. Accordingly, by making the amount of the axial run-outno more than 0.1 mm as in this embodiment, the fore and aft vibrationcan be made no more than 0.1 G.

As understood from the above description, in this second embodiment,when the crankshaft 1 is rotated, the flywheel body 5 is ensured torotate with the crankshaft 1 by means of the large circumferentialrigidity of the elastic plate 2. Since the amount of the axial run-outof the radial engaging surface 5g is no more than 0.1 mm, the engagementbetween the radial engaging surface 5g and the clutch facing 8 isperformed quite smoothly, so that the fore and aft vibration does notexceed 0.1 G. Accordingly, the driving power is transmitted from theengine to the transmission without giving the uncomfortable feeling tothe human body.

It is to be appreciated that in this second embodiment, the axialrigidity of the elastic plate 2 is not necessarily selected at 600 kg/mmto 2200 kg/mm.

It is to be understood that the invention is not to be limited to theembodiments described above, and that various changes and modificationsmay be made without departing from the spirit and scope of the inventionas defined in the appended claims.

1. A flywheel for a power transmission system for transmitting enginetorque to a driven unit, comprising: an elastic plate secured to acrankshaft to rotate therewith; a flywheel body secured to said elasticplate and having an engageable surface for engaging with a clutch disc;and a reinforcing member for reinforcing said elastic plate at a portionof said elastic plate which is secured to said crankshaft; said elasticplate having an axial rigidity in the range of 600 kg/mm to 2200 kg/mmso as to ensure transmission of engine torque to said driven unit, whiledecreasing noise produced by a bending vibration of said crankshaft;wherein each of said elastic plate, said flywheel body and saidreinforcing member comprises a first portion, said first portion of saidflywheel body being placed axially between said first portion of saidelastic plate and said reinforcing member, and said first portions ofsaid elastic plate, said flywheel body and said reinforcing memberdefining clearances for allowing said first portion of said flywheelbody to move axially between said first portions of said elastic plateand said reinforcing member.
 2. A flywheel as set forth in claim 1,wherein said axial rigidity is in the range of 600 kg/mm to 1700 kg/mm.3. A flywheel as set forth in claim 2, wherein an axial run-out of saidengageable surface when rotated by said crankshaft is no more than 0.1mm.
 4. A flywheel according to claim 1, wherein said reinforcing member(4) and said elastic plate (2) are fastened to said crankshaft (1) by afastening means (3), and said elastic plate is clamped between saidcrankshaft and said reinforcing member.
 5. A flywheel according to claim4, wherein said elastic plate is circular and comprises an outerperipheral portion (2b) surrounding said first portion of said elasticplate, so that said first portion of said elastic plate is an innerportion of said elastic plate, said flywheel body comprises an outerperipheral portion (5a) which surrounds said first portion of saidflywheel body, so that said first portion of said flywheel body is aninner portion of said flywheel body, said outer peripheral portions ofsaid elastic plate and said flywheel body are fastened together by asecond fastening means (6), said inner portion of said flywheel bodycomprises an inwardly facing inside cylindrical surface defining acentral circular hole (5b), said reinforcing member comprises acylindrical portion (4a) which is received in said circular hole (5b) ofsaid flywheel body, and comprises an outwardly facing outsidecylindrical surface surrounded by said inwardly facing cylindricalsurface of said flywheel body, said first portion of said reinforcingmember is in the form of an outward flange (4b), said first portion ofsaid flywheel body is slidably mounted on said cylindrical portion ofsaid reinforcing member so that said first portion of said flywheel bodyis axially slidable between said inner portion of said elastic plate andsaid outward flange of said reinforcing member.
 6. A flywheel accordingto claim 4, wherein said inner portion of said flywheel body comprises afirst surface (5f) which is substantially parallel to said engageablesurface (5g) and which faces toward said elastic plate, and a secondsurface (5d) which is substantially parallel to said engageable surfaceand which faces toward said outward flange of said reinforcing member,said inner portion of said elastic plate comprising an abutting surfaceconfronting said first surface of said flywheel body and limiting anaxial movement of said inner portion of said elastic plate by abuttingagainst said first surface of said flywheel body, said outward flange ofsaid reinforcing member comprises an abutting surface confronting saidsecond surface of said flywheel body and limiting the axial movement ofsaid inner portion of said flywheel body by abutting against said secondsurface of said flywheel body, an axial distance between said first andsecond surfaces of said flywheel body is smaller than an axial distancebetween said abutting surfaces of said elastic member and saidreinforcing member.
 7. A flywheel according to claim 6, wherein saidsecond surface (5d) of said inner portion of said flywheel body islocated axially between said first surface (5f) and said engageablesurface (5g) of said flywheel body.
 8. A flywheel for a powertransmission system for transmitting engine torque to a driven unit,comprising: an elastic plate secured to a crankshaft to rotatetherewith; a flywheel body secured to said elastic plate and having anengageable surface for engaging with a clutch disc; and a reinforcingmember for reinforcing said elastic plate at a portion of said elasticplate which is secured to said crankshaft; and said engageable surfacehaving an axial run-out which is equal to or less than 0.1 mm; whereineach of said elastic plate, said flywheel body and said reinforcingmember comprises a first portion, said first portion of said flywheelbody being placed axially between said first portions of said elasticplate and said reinforcing member, and said first portions of saidelastic plate, said flywheel body and said reinforcing member definingclearances for allowing said first portion of said flywheel body to moveaxially between said first portions of said elastic plate and saidreinforcing member.
 9. A flywheel assembly comprising: a driving shaft(1) for transmitting torque; a circular elastic member (2) comprising anouter portion and an inner portion and extending radially inwardly fromsaid outer portion to said inner portion, said inner portion of saidelastic member being fastened to a shaft end of said driving shaft; anannular flywheel member (5) comprising an outer portion and an innerportion and extending radially inwardly from said outer portion to saidinner portion of said flywheel member, said outer portion of saidflywheel member being fastened to said outer portion of said elasticmember, said inner portion of said flywheel member comprising a centralcircular hole; and a reinforcing member (4) comprising a cylindricalportion (4a) axially extending from a first end to a second end, aninner portion extending radially inwardly from said first end of saidcylindrical portion, and an outward flange (4b) extending radiallyoutwardly from said second end of said cylindrical portion, said innerportion of said reinforcing member being fastened to said shaft end ofsaid driving shaft, said cylindrical portion of said reinforcing memberbeing fit in said circular hole of said flywheel member with a clearanceto form a loose fit; wherein said inner portion of said elastic memberis fixedly clamped between said shaft end of said driving shaft and saidinner portion of said reinforcing member, said inner portion of saidflywheel member is loosely fit over said cylindrical portion of saidreinforcing member and located axially between said inner portion ofsaid elastic member and said outward flange of said reinforcing member,said outward flange is axially spaced from said inner portion of saidelastic member at an axial distance which allows axial movement of saidinner portion of said flywheel body between said inner portion of saidelastic member and said outward flange of said reinforcing member.
 10. Aflywheel assembly according to claim 3, wherein said elastic member hasan axial rigidity which is in the range of 600 kg/mm to 2200 kg/mm. 11.A flywheel assembly according to claim 9, wherein a wall thickness ofsaid inner portion of said reinforcing member is greater than a wallthickness of each of said outward flanges of said reinforcing member andsaid inner portion of said elastic member, said wall thickness of eachof said inner portion and said outward flange of said reinforcing memberand said inner portion of said elastic member being a dimension measuredin an axial direction parallel to an axis of said driving shaft.
 12. Aflywheel assembly according to claim 9, further comprising a firstfastening means for fastening said outer portions of said elastic memberand said flywheel member together, and a second fastening means forfastening said inner portions of said elastic member and saidreinforcing member to said shaft end of said driving shaft, each of saidfirst and second fastening means comprises screw fasteners extendingaxially along an axis of said driving shaft.
 13. A flywheel assembly fora power transmission system for transmitting engine torque, comprising:an elastic plate secured to a crankshaft to rotate therewith; a flywheelbody secured to said elastic plate and having an engaging surface forengaging with a clutch disc; and a reinforcing member for reinforcingsaid elastic plate at a portion of said elastic plate which is securedto said crankshaft; said elastic plate having an axial rigidity in therange of 600 kg/mm to 2200 kg/mm so as to ensure transmission of enginetorque through said flywheel assembly while decreasing noise produced bya bending vibration of said crankshaft; wherein each of said elasticplate, said flywheel body and said reinforcing member comprises a firstportion, said first portion of said flywheel body being placed axiallybetween said first portions of said elastic plate and said reinforcingmember, and said first portions of said elastic plate, said flywheelbody and said reinforcing member defining clearances for allowing saidfirst portion of said flywheel body to move axially between said firstportions of said elastic plate and said reinforcing member.
 14. Aflywheel assembly as set forth in claim 13, wherein said axial rigidityis in the range of 600 kg/mm to 1700 kg/mm.
 15. A flywheel assembly asset forth in claim 14, wherein an axial run-out of said engaging surfacewhen rotated by said crankshaft is no more than 0.1 mm.
 16. A flywheelassembly according to claim 13, wherein said reinforcing member ( 4 )and said elastic plate ( 2 ) are fastened to said crankshaft ( 1 ) by afastening means ( 3 ), and said elastic plate is clamped between saidcrankshaft and said reinforcing member.
 17. A flywheel assemblyaccording to claim 16, wherein said elastic plate is circular andcomprises an outer peripheral portion ( 2b) surrounding said firstportion of said elastic plate, so that said first portion of saidelastic plate is an inner portion of said elastic plate, said flywheelbody comprises an outer peripheral portion ( 5a) which surrounds saidfirst portion of said flywheel body, so that said first portion of saidflywheel body is an inner portion of said flywheel body, said outerperipheral portions of said elastic plate and said flywheel body arefastened together by a second fastening means ( 6 ), said inner portionof said flywheel body comprises an inwardly facing inside cylindricalsurface defining a central circular hole ( 5b), said reinforcing membercomprises a cylindrical portion ( 4a) which is received in said circularhole ( 5b) of said flywheel body, and comprises an outwardly facingoutside cylindrical surface surrounded by said inwardly facingcylindrical surface of said flywheel body, said first portion of saidreinforcing member is in the form of an outward flange ( 4b), said firstportion of said flywheel body is mounted on said cylindrical portion ofsaid reinforcing member, and said cylindrical portion of saidreinforcing member is sized to allow said first portion of said flywheelbody to slide axially between said inner portion of said elastic plateand said outward flange of said reinforcing member.
 18. A flywheelassembly according to claim 16, wherein said inner portion of saidflywheel body comprises a first surface ( 5f) which is substantiallyparallel to said engaging surface ( 5g) and which faces toward saidelastic plate, and a second surface ( 5d) which is substantiallyparallel to said engaging surface and which faces toward said outwardflange of said reinforcing member, said inner portion of said elasticplate comprising an abutting surface confronting said first surface ofsaid flywheel body and limiting an axial movement of said inner portionof said flywheel body by abutting against said first surface of saidflywheel body, said outward flange of said reinforcing member comprisesan abutting surface confronting said second surface of said flywheelbody and limiting the axial movement of said inner portion of saidflywheel body by abutting against said second surface of said flywheelbody, an axial distance between said first and second surfaces of saidflywheel body is smaller than an axial distance between said abuttingsurfaces of said elastic member and said reinforcing member.
 19. Aflywheel assembly according to claim 18, wherein said second surface (5d) of said inner portion of said flywheel body is located axiallybetween said first surface ( 5f) and said engaging surface ( 5g) of saidflywheel body.
 20. A flywheel assembly for a power transmission systemfor transmitting engine torque, comprising: an elastic plate secured toa crankshaft to rotate therewith; a flywheel body secured to saidelastic plate and having an engaging surface for engaging with a clutchdisc; and a reinforcing member for reinforcing said elastic plate at aportion of said elastic plate which is secured to said crankshaft; andsaid engaging surface having an axial run-out which is equal to or lessthan 0.1 mm; wherein each of said elastic plate, said flywheel body andsaid reinforcing member comprises a first portion, said first portion ofsaid flywheel body being placed axially between said first portions ofsaid elastic plate and said reinforcing member, and said first portionsof said elastic plate, said flywheel body and said reinforcing memberdefining clearances for allowing said first portion of said flywheelbody to move axially between said first portions of said elastic plateand said reinforcing member.
 21. A flywheel assembly comprising: acrankshaft ( 1 ) for transmitting torque; a circular elastic plate ( 2 )comprising an outer portion and an inner portion and extending radiallyinwardly from said outer portion to said inner portion, said innerportion of said elastic plate being fastened to a shaft end of saidcrankshaft; an annular flywheel body ( 5 ) comprising an outer portionand an inner portion and extending radially inwardly from said outerportion to said inner portion of said flywheel body, said outer portionof said flywheel body being fastened to said outer portion of saidelastic plate, said inner portion of said flywheel body comprising acentral circular hole; and a reinforcing member ( 4 ) comprising acylindrical portion ( 4a) axially extending from a first member end to asecond member end, an inner portion extending radially inwardly fromsaid first member end of said cylindrical portion, and an outward flange( 4b) extending radially outwardly from said second member end of saidcylindrical portion, said inner portion of said reinforcing member beingfastened to said shaft end of said crankshaft, said cylindrical portionof said reinforcing member being fit in said circular hole of saidflywheel body with a clearance to form a loose fit; wherein said innerportion of said elastic plate is fixedly clamped between said shaft endof said crankshaft and said inner portion of said reinforcing member,said inner portion of said flywheel body is fit over said cylindricalportion of said reinforcing member and located axially between saidinner portion of said elastic plate and said outward flange of saidreinforcing member, said outward flange is axially spaced from saidinner portion of said elastic plate at an axial distance which allowsaxial movement of said inner portion of said flywheel body between saidinner portion of said elastic plate and said outward flange of saidreinforcing member.
 22. A flywheel assembly according to claim 21,wherein said elastic plate has an axial rigidity which is in the rangeof 600 kg/mm to 2200 kg/mm.
 23. A flywheel assembly according to claim21, wherein a wall thickness of said inner portion of said reinforcingmember is greater than a wall thickness of each of said outward flangeof said reinforcing member and said inner portion of said elastic platesaid wall thickness of each of said inner portion and said outwardflange of said reinforcing member and said inner portion of said elasticplate being a dimension measured in an axial direction parallel to anaxis of said crankshaft.
 24. A flywheel assembly according to claim 21,further comprising a first fastening means for fastening said outerportions of said elastic plate and said flywheel body together, and asecond fastening means for fastening said inner portions of said elasticplate and said reinforcing member to said shaft end of said crankshaft,each of said first and second fastening means comprises screw fastenersextending axially along an axis of said crankshaft.
 25. A flywheelassembly for a power transmission system for transmitting engine torquecomprising: a crankshaft; an elastic plate comprising an inner portionsecured to a shaft end of said crankshaft; a flywheel body secured tosaid elastic plate and having an engaging surface for engaging with theclutch disc; and a reinforcing member for reinforcing said elastic plateat said inner portion of said elastic plate; wherein said elastic platehas an axial rigidity in the range of 600 kg/mm to 2200 kg/mm so as toensure transmission of engine torque through said flywheel assembly,while decreasing noise produced by a bending vibration of saidcrankshaft; wherein said elastic plate is clamped axially between saidreinforcing member and said shaft end of said crankshaft, and wherein afirst portion of said flywheel moves axially with respect to saidreinforcing member and said elastic plate, wherein said reinforcingmember has a radially extending portion which extends at least inwardlyof said flywheel body, and wherein said elastic plate comprises a firstportion, said first portion of said flywheel body being placed axiallyafter said first portion of said elastic plate, and said first portionsof said flywheel body and said elastic plate defining a first clearanceand said flywheel body having a first free space on a side opposite ofthe first clearance for allowing said first portion of said flywheelbody to move axially within the first clearance and the free space. 26.A flywheel assembly as set forth in claim 25, wherein said flywheel bodycomprises an inner portion defining a circular central hole, and anouter portion surrounding said inner portion of said flywheel body; saidelastic plate comprises an outer portion which surrounds said innerportion of said elastic plate and which is fixed to said outer portionof said flywheel body; said reinforcing member is fit in said centralhole of said flywheel body with a clearance to form a loose fit; andsaid reinforcing member comprises an outer circumferential surface forallowing said inner portion of said flywheel body to move axially tosaid elastic plate without limiting an axial movement of the innerpotion of said flywheel body toward said elastic plate.
 27. A flywheelassembly as set forth in claim 26, wherein said reinforcing memberextends axially from a first member end defined by a radially extendingabutment surface held in contact with said elastic plate, to a secondmember end; said outer circumferential surface of said reinforcingmember extends from said abutment surface toward said second member endof said reinforcing member; said outer circumferential surface of saidreinforcing member comprises an outer cylindrical surface section fit insaid central hole of said flywheel body, and an outer curved surfacesection which extends continuously from said outer cylindrical surfacesection to said abutment surface; and said curved surface section is asurface of revolution whose diameter decreases continuously from adiameter of said cylindrical surface section toward said abutmentsurface.
 28. A flywheel assembly as set forth in claim 27, wherein saidflywheel body comprises a side surface facing toward said elastic plate,and said engaging surface which faces away from said elastic plate andwhich extends in an imaginary flat plane; and said second member end ofsaid reinforcing member is located axially between said engaging surfaceand said side surface of said flywheel body and away from said imaginaryflat plane.
 29. A flywheel assembly as set forth in claim 25, whereinsaid flywheel body comprises an inner portion defining a circularcentral hole, and an outer portion surrounding said inner portion ofsaid flywheel body; said elastic plate comprises an outer portion whichsurrounds said inner portion of said elastic plate and which is fixed tosaid outer portion of said flywheel body; and said reinforcing membercomprises an outer circumferential surface allowing said inner portionof said flywheel body to move axially toward said elastic plate withoutlimiting an axial movement of the inner portion of said flywheel bodytoward said elastic plate.
 30. A flywheel assembly as set forth in claim25, wherein said flywheel body comprises a side surface facing towardsaid elastic plate, and said engaging surface which faces away from saidelastic plate; and said reinforcing member comprises a radiallyextending abutment surface held in contact with said elastic plate, andan outer circumferential curved surface which extends continuously fromsaid abutment surface to a curved surface end which is located axiallybetween said side surface of said flywheel body and said engagingsurface of said flywheel body.
 31. A flywheel assembly as set forth inclaim 30, wherein said outer circumferential curved surface of saidreinforcing member is a surface of revolution whose diameter increasescontinuously from said abutment surface of said reinforcing member tosaid curved surface end of said outer circumferential curved surface.32. A flywheel assembly as set forth in claim 30, wherein saidreinforcing member extends axially from a first member end defined bysaid abutment surface to a second member end which is located axiallybetween said engaging surface and said side surface of said flywheelbody; and an axial distance of said second member end of saidreinforcing member from said abutment surface of said reinforcing memberis smaller than an axial distance of said engaging surface of saidflywheel body from said abutment surface of said reinforcing member. 33.A flywheel assembly as set forth in claim 30, wherein said engagingsurface of said flywheel body extends in an imaginary flat plane; andsaid reinforcing member extends axially from a first member end definedby said abutment surface to a second member end which is located axiallybetween said engaging surface and said side surface of said flywheelbody and which is away from said imaginary flat plane.
 34. A flywheelassembly as set forth in claim 30, wherein said flywheel body comprisesan inner portion defining a circular central hole, and an outer portionsurrounding said inner portion of said flywheel body; said elastic platecomprises an outer portion which surrounds said inner portion of saidelastic plate and which is fixed to said outer portion of said flywheelbody; said reinforcing member comprises a received portion which isreceived in said central hole of said flywheel body; and said outercurved surface of said reinforcing member extends continuously from saidabutment surface to said received portion.
 35. A flywheel assembly asset forth in claim 34, wherein said received portion of said reinforcingmember comprises a cylindrical outside surface received in said centralhole of said flywheel body, and the diameter of said curved surfaceincreases continuously from said abutment surface to a diameter of saidcylindrical surface of said reinforcing member.
 36. A flywheel assemblyas set forth in claim 33, wherein said axial rigidity is in the range of600 kg/mm to 1700 kg/mm.
 37. A flywheel assembly as set forth in claim33, wherein an axial run-out of said engaging surface when rotated bysaid crankshaft is no more than 0.1 mm.
 38. A flywheel assembly as setforth in claim 37, wherein said engaging surface of said flywheel bodyis formed so as to make the axial run-out no more than 0.1 mm byprocessing said engaging surface of said flywheel body in an assembledstate in which said crankshaft, said elastic plate, said flywheel bodyand said reinforcing member are assembled in a unit.
 39. A flywheelassembly as set forth in claim 33, wherein said side surface of saidflywheel body comprises an outer side surface section which faces towardsaid elastic plate and which is fastened to an outer portion of saidelastic plate and an inner side surface section which faces toward saidelastic plate, which is surrounded by said outer side surface section ofsaid flywheel body, and which is raised from said outer side surfacesection axially toward said elastic plate.
 40. A flywheel assemblyaccording to claim 25, wherein said first portions of said flywheel bodyand said elastic plate define a space consisting essentially of saidfirst clearance.
 41. A flywheel assembly according to claim 25, whereinsaid first portion of said flywheel body slidably contacts an axialsurface of said radially extending portion of said reinforcing member.42. A flywheel assembly according to claim 25, wherein said flywheelbody axially moves corresponding to said axial rigidity of said elasticplate in the range of 600 kg/mm to 2200 kg/mm without contact on itsradial surfaces when said flywheel is engaged and disengaged.
 43. Aflywheel assembly as set forth in claim 25, wherein said axial rigidityis in the range of 600 kg/mm to 1700 kg/mm.
 44. A flywheel assembly asset forth in claim 43, wherein an axial run-out of said engaging surfacewhen rotated by said crankshaft is no more than 0.1 mm.
 45. A flywheelassembly according to claim 25, wherein said elastic plate is clampedaxially between said reinforcing member and said shaft end of saidcrankshaft by a fastening means.
 46. A flywheel assembly according toclaim 25, wherein said elastic plate is circular and comprises an outerperipheral portion ( 2b) surrounding said first portion of said elasticplate, so that said first portion of said elastic plate is an innerportion of said elastic plate, said flywheel body comprises an outerperipheral portion ( 5a) which surrounds said first portion of saidflywheel body, so that said first portion of said flywheel body is aninner portion of said flywheel body, said outer peripheral portions ofsaid elastic plate and said flywheel body are fastened together by asecond fastening means ( 6 ), said inner portion of said flywheel bodycomprises an inwardly facing inside cylindrical surface defining acentral circular hole ( 5b), said reinforcing member comprises acylindrical portion ( 4a) which is received in said circular hole ( 5b)of said flywheel body, and comprises an outwardly facing outsidecylindrical surface surrounded by said inwardly facing cylindricalsurface of said flywheel body.
 47. A flywheel assembly according toclaim 46, wherein said inner portion of said flywheel body comprises afirst surface ( 5f) which is parallel to said engaging surface ( 5g) andwhich faces toward said elastic plate, and a second surface ( 5d) whichis parallel to said engaging surface, said inner portion of said elasticplate comprising an abutting surface confronting said first surface ofsaid flywheel body and limiting an axial movement of said inner portionof said flywheel body by abutting against said first surface of saidflywheel body.
 48. A flywheel assembly according to claim 47, whereinsaid second surface ( 5d) of said inner portion of said flywheel body islocated axially between said first surface ( 5f) and said engagingsurface ( 5g) of said flywheel body.
 49. A flywheel assembly as setforth in claim 25, wherein: said elastic plate is a circular elasticplate ( 2 ) which further comprises an outer portion, and said innerportion extends radially inwardly from said outer portion to said innerportion; said fly wheel body is an annular flywheel body ( 5 ) whichcomprises an outer portion and an inner portion and extending radiallyinwardly from said outer portion to said inner portion of said flywheelbody, said outer portion of said flywheel body being fastened to saidouter portion of said elastic plate, said inner portion of said flywheelbody comprising a central circular hole; and said reinforcing memberfurther comprises a cylindrical portion ( 4a) axially extending from afirst member end to a second member end, an inner portion extendingradially inwardly from said first member end of said cylindricalportion, and an outward flange ( 4b) extending radially outwardly fromsaid second member end of said cylindrical portion, said inner portionof said reinforcing member being fastened to said shaft end of saidcrankshaft, said cylindrical portion of said reinforcing member beingfit in said circular hole of said flywheel body with a clearance to forma loose fit; wherein said inner portion of said elastic plate is fixedlyclamped between said shaft end of said crankshaft and said inner portionof said reinforcing member, said inner portion of said flywheel body isfit over said cylindrical portion of said reinforcing member.
 50. Aflywheel assembly according to claim 49, wherein a wall thickness ofsaid inner portion of said reinforcing member is greater than a wallthickness of each of said outward flange of said reinforcing member andsaid inner portion of said elastic plate, said wall thickness of each ofsaid inner portion and said outward flange of said reinforcing memberand said inner portion of said elastic plate being a dimension measuredin an axial direction parallel to an axis of said crankshaft.
 51. Aflywheel assembly according to claim 49, further comprising a firstfastening means for fastening said outer portions of said elastic plateand said flywheel body together, and a second fastening means forfastening said inner portions of said elastic plate and said reinforcingmember to said shaft end of said crankshaft, each of said first andsecond fastening means comprises screw fasteners extending axially alongan axis of said crankshaft.
 52. A flywheel assembly according to claim25, wherein said radially extending portion further comprises a radiallyextending section ( 4b) at least partially overlapping the first portionof said flywheel body in a radial direction.
 53. A flywheel assemblyflywheel assembly of a power transmission system for transmitting enginetorque, said flywheel assembly comprising: a crankshaft; an elasticplate comprising an inner portion secured to a shaft end of saidcrankshaft; a flywheel body secured to said elastic plate and having anengaging surface for engaging with the clutch disc; and a reinforcingmember for reinforcing said elastic plate at said inner portion of saidelastic plate; wherein said engaging surface has an axial run-out whichis no more than 0.1 mm; wherein said elastic plate is clamped axiallybetween said reinforcing member and said shaft end of said crankshaft,and wherein a first portion of said flywheel moves axially with respectto said reinforcing member and said elastic plate, wherein saidreinforcing member has a radially extending portion which extends atleast inwardly of said flywheel body, and wherein said elastic platecomprises a first portion, said first portion of said flywheel bodybeing placed axially after said first portion of said elastic plate, andsaid first portions of said flywheel body and said elastic platedefining a first clearance, and said flywheel body having a first freespace on a side opposite of the flywheel facing the elastic plate forallowing said first portion of said flywheel body to move axially withinthe first clearance and the free space.
 54. A flywheel assembly asclaimed in 53, wherein said flywheel body comprises an inner portiondefining a circular central hole, and an outer portion surrounding saidinner portion of said flywheel body; said elastic plate comprises anouter portion which surrounds said inner portion of said elastic plateand which is fixed to said outer portion of said flywheel body; saidreinforcing member is fit in said central hole of said flywheel bodywith a clearance to form a loose fit; and said reinforcing membercomprises an outer circumferential surface for allowing said innerportion of said flywheel body to move axially to said elastic platewithout limiting an axial movement of the inner portion of said flywheelbody toward said elastic plate.
 55. A flywheel assembly as set forth inclaim 54, wherein said reinforcing member extends axially from a firstmember end defined by a radially extending abutment surface held incontact with said elastic plate, to a second member end; said outercircumferential surface of said reinforcing member extends continuouslyfrom said abutment surface toward said second member end of saidreinforcing member; said outer circumferential surface of saidreinforcing member comprises an outer cylindrical surface section fit insaid central hole of said flywheel body, and an outer curved surfacesection which extends continuously from said outer cylindrical surfacesection to said abutment surface; and said curved surface section is asurface of revolution whose diameter decreases from a diameter of saidcylindrical surface section toward said abutment surface.
 56. A flywheelassembly as set forth in claim 55, wherein said flywheel body comprisesa side surface facing toward said elastic plate, and said engagingsurface which faces away from said elastic plate and which extends in animaginary flat plane; and said second member end of said reinforcingmember is located axially between said engaging surface and said sidesurface of said flywheel body and away from said imaginary flat plane.57. A flywheel assembly as set forth in claim 53, wherein said flywheelbody comprises an inner portion defining a circular central hole, and anouter portion surrounding said inner portion of said flywheel body; saidelastic plate comprises an outer portion which surrounds said innerportion of said elastic plate and which is fixed to said outer portionof said flywheel body; and said reinforcing member comprises an outercircumferential surface allowing said inner portion of said flywheelbody to move axially toward said elastic plate without limiting an axialmovement of the inner portion of said flywheel body toward said elasticplate.
 58. A flywheel assembly as set forth in claim 53, wherein saidflywheel body comprises a side surface facing toward said elastic plate,and said engaging surface which faces away from said elastic plate; andsaid reinforcing member comprises a radially extending abutment surfaceheld in contact with said elastic plate, and an outer circumferentialcurved surface which extends continuously from said abutment surface toa curved surface end which is located axially between said side surfaceof said flywheel body and said engaging surface of said flywheel body.59. A flywheel assembly as set forth in claim 58, wherein said outercircumferential curved surface of said reinforcing member is a surfaceof revolution whose diameter increases from said abutment surface ofsaid reinforcing member to said curved surface end of said outercircumferential curved surface.
 60. A flywheel assembly as set forth inclaim 58, wherein said reinforcing member extends axially from a firstmember end defined by said abutment surface to a second member end whichis located axially between said engaging surface and said side surfaceof said flywheel body; and an axial distance of said second member endof said reinforcing member from said abutment surface of saidreinforcing member is smaller than an axial distance of said engagementsurface of said flywheel body from said abutment surface of saidreinforcing member.
 61. A flywheel assembly as set forth in claim 58,wherein said engaging surface of said flywheel body extends in animaginary flat plane; and said reinforcing member extends axially from afirst member end defined by said abutment surface to a second member endwhich is located axially between said engaging surface and said sidesurface of said flywheel body and which is away from said imaginary flatplane.
 62. A flywheel assembly as set forth in claim 61, wherein saidflywheel body comprises an inner portion defining a circular centralhole, and an outer portion surrounding said inner portion of saidflywheel body; said elastic plate comprises an outer portion whichsurrounds said inner portion of said elastic plate and which is fixed tosaid outer portion of said flywheel body; said reinforcing membercomprises a received portion which is received in said central hole ofsaid flywheel body; and said outer curved surface of said reinforcingmember extends continuously from said abutment surface to said receivedportion.
 63. A flywheel assembly as set forth in claim 62, wherein saidreceived portion of said reinforcing member comprises a cylindricaloutside surface received in said central hole of said flywheel body, andthe diameter of said curved surface increases continuously from saidabutment surface to a diameter of said cylindrical surface of saidreinforcing member.
 64. A flywheel assembly as set forth in claim 61,wherein said engaging surface of said flywheel body is formed so as tomake the axial run-out no more than 0.1 mm by processing said engagingsurface of said flywheel body in an assembled state in which saidcrankshaft, said elastic plate, said flywheel body and said reinforcingmember are assembled in a unit.
 65. A flywheel assembly according toclaim 53, wherein said first portions of said flywheel body and saidelastic plate define a space consisting essentially of said firstclearance.
 66. A flywheel assembly according to claim 53, wherein saidfirst portion of said flywheel body slidably contacts an axial surfaceof said radially extending portion of said reinforcing member.
 67. Aflywheel assembly according to claim 53, wherein said elastic plate hasan axial rigidity in the range of 600 kg/mm to 2200 kg/mm so as toensure transmission of engine torque through said flywheel assembly,while decreasing noise produced by a bending vibration of saidcrankshaft; and wherein said flywheel body axially moves correspondingto said axial rigidity of said elastic plate in the range of 600 kg/mmto 2200 kg/mm without contact on its radial surfaces when said flywheelis engaged and disengaged.
 68. A flywheel assembly as set forth in claim53, wherein said elastic plate has an axial rigidity in the range of 600kg/mm to 2200 kg/mm so as to ensure transmission of engine torquethrough said flywheel assembly, while decreasing noise produced by abending vibration of said crankshaft.
 69. A flywheel assembly accordingto claim 68, wherein said elastic plate is clamped axially between saidreinforcing member and said shaft end of said crankshaft by a fasteningmeans.
 70. A flywheel assembly according to claim 68, wherein saidelastic plate has an axial rigidity which is in the range of 600 kg/mmto 1700 kg/mm.
 71. A flywheel assembly according to claim 53, whereinsaid elastic plate is circular and comprises an outer peripheral portion( 2b) surrounding said first portion of said elastic plate, so that saidfirst portion of said elastic plate is an inner portion of said elasticplate, said flywheel body comprises an outer peripheral portion ( 5a)which surrounds said first portion of said flywheel body, so that saidfirst portion of said flywheel body is an inner portion of said flywheelbody, said outer peripheral portions of said elastic plate and saidflywheel body are fastened together by a second fastening means ( 6 ),said inner portion of said flywheel body comprises an inwardly facinginside cylindrical surface defining a central circular hole ( 5b), saidreinforcing member comprises a cylindrical portion ( 4a) which isreceived in said circular hole ( 5b) of said flywheel body, andcomprises an outwardly facing outside cylindrical surface surrounded bysaid inwardly facing cylindrical surface of said flywheel body.
 72. Aflywheel assembly according to claim 71, wherein said inner portion ofsaid flywheel body comprises a first surface ( 5f) which is parallel tosaid engaging surface ( 5g) and which faces toward said elastic plate,and a second surface ( 5d) which is parallel to said engaging surface,said inner portion of said elastic plate comprising an abutting surfaceconfronting said first surface of said flywheel body and limiting anaxial movement of said inner portion of said flywheel body by abuttingagainst said first surface of said flywheel body.
 73. A flywheelassembly according to claim 72, wherein said second surface ( 5d) ofsaid inner portion of said flywheel body is located axially between saidfirst surface ( 5f) and said engaging surface ( 5g) of said flywheelbody.
 74. A flywheel assembly as set forth in claim 53, wherein: saidelastic plate is a circular elastic plate ( 2 ) which further comprisesan outer portion, and said inner portion extends radially inwardly fromsaid outer portion to said inner portion; said fly wheel body is anannular flywheel body ( 5 ) which comprises an outer portion and aninner portion and extending radially inwardly from said outer portion tosaid inner portion of said flywheel body, said outer portion of saidflywheel body being fastened to said outer portion of said elasticplate, said inner portion of said flywheel body comprising a centralcircular hole; and said reinforcing member further comprises acylindrical portion ( 4a) axially extending from a first member end to asecond member end, an inner portion extending radially inwardly fromsaid first member end of said cylindrical portion, and an outward flange( 4b) extending radially outwardly from said second member end of saidcylindrical portion, said inner portion of said reinforcing member beingfastened to said shaft end of said crankshaft, said cylindrical portionof said reinforcing member being fit in said circular hole of saidflywheel body with a clearance to form a loose fit; wherein said innerportion of said elastic plate is fixedly clamped between said shaft endof said crankshaft and said inner portion of said reinforcing member,said inner portion of said flywheel body is fit over said cylindricalportion of said reinforcing member.
 75. A flywheel assembly according toclaim 74, wherein a wall thickness of said inner portion of saidreinforcing member is greater than a wall thickness of each of saidoutward flange of said reinforcing member and said inner portion of saidelastic plate, said wall thickness of each of said inner portion andsaid outward flange of said reinforcing member and said inner portion ofsaid elastic plate being a dimension measured in an axial directionparallel to an axis of said crankshaft.
 76. A flywheel assemblyaccording to claim 74, further comprising a first fastening means forfastening said outer portions of said elastic plate and said flywheelbody together, and a second fastening means for fastening said innerportions of said elastic plate and said reinforcing member to said shaftend of said crankshaft, each of said first and second fastening meanscomprises screw fasteners extending axially along an axis of saidcrankshaft.
 77. A flywheel assembly according to claim 53, wherein saidradially extending portion further comprises a radially extendingsection ( 4b) at least partially overlapping the first portion of saidflywheel body in a radial direction.